Nice one V, that's a great result for only 20 mins. And a 2x2 experiment!? Way cool!
Have you looked at freebies like telescopius to post the full size?
How are you calculating exposure time?
The internal (eternal?) struggle with saturation seems to be a rite of passage? Quite often I'm finding my final tweak is to desaturate, sometimes quite a lot. It was definitely a surprise to me that I've had to fight it.